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LDL cholesterol: “The bad cholesterol”

When doctors talk about cholesterol concerns, they usually mean the so-called bad cholesterol: LDL.

LDL cholesterol collects in the walls of blood vessels, causing the blockages of atherosclerosis. Higher LDL levels put you at greater risk of a heart attack from a sudden blood clot in an artery narrowed by atherosclerosis.

Getting your LDL cholesterol checked helps determine your risk of heart disease. If your LDL cholesterol is high, treatment can reduce your chance of having a heart attack.

LDL cholesterol: What is it?

Cholesterol isn’t all bad. It’s an essential fat that provides support in the membranes of our bodies’ cells. Some cholesterol comes from diet, and some is made by the liver. Cholesterol can’t dissolve in blood, so transport proteins carry it where it needs to go. These carriers are called lipoproteins, and LDL (low-density lipoprotein) is one member of the lipoprotein family.

Acting like a microscopic bus fleet, lipoproteins pick up and carry loads of cholesterol through the blood. Each form of lipoprotein has different preferences for cholesterol, and behaves differently with the cholesterol it carries.

An LDL particle is a microscopic blob consisting of an outer rim of lipoprotein surrounding a cholesterol centre. LDL is called low-density lipoprotein because LDL particles tend to be less dense than other kinds of cholesterol particles.

LDL cholesterol: What makes bad cholesterol bad

LDL cholesterol can’t help being bad - it’s just its chemical makeup. LDL cholesterol is an important part of the process of narrowing arteries, called atherosclerosis.

  • Some LDL cholesterol circulating through the bloodstream tends to deposit in the walls of arteries. This process starts as early as childhood or adolescence.
  • White blood cells swallow and try to digest the LDL, possibly in an attempt to protect the blood vessels.
  • In the process, the white blood cells convert the LDL to a toxic (oxidised) form.
  • More white blood cells and other cells migrate to the area, creating steady low-grade inflammation in the artery wall.
  • Over time, more LDL cholesterol and cells collect in the area. The ongoing process creates a bump in the artery wall called a plaque. The plaque is made of cholesterol, cells, and debris.
  • The process tends to continue, growing the plaque and slowly blocking the artery.

An even greater danger than slow blockage is a sudden rupture of the surface of the plaque. A blood clot can form on the plaque, causing a heart attack.

What LDL cholesterol test results mean

Although heart attacks are unpredictable, higher levels of LDL cholesterol increase your risk.

Expert groups define the levels of LDL cholesterol as follows:

  • An LDL of less than 3.0 millimoles per litre (mmol/l) of blood is optimal for those not at high risk of heart disease.
  • For people at high risk of heart disease, or with known heart disease, LDL less than 2.0 mmol/l is advised.
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